The present invention generally relates to fuel injector drive circuitry and, more particularly, relates to a drive circuit for a piezoelectric fuel injector.
Automotive vehicle engines are generally equipped with fuel injectors for injecting fuel (e.g., gasoline or diesel fuel) into the individual cylinders or intake manifold of the engine. The engine fuel injectors are coupled to a fuel rail which contains high pressure fuel that is delivered by way of a fuel delivery system. Conventional fuel injectors typically employ a valve that is actuated to open and close to control the amount of fluid fuel metered from the fuel rail and injected into the corresponding engine cylinder or intake manifold.
One type of fuel injector that offers precise metering of fuel is the piezoelectric fuel injector. Piezoelectric fuel injectors employ piezoelectric actuators for opening and closing an injection valve to meter fuel injected into the engine. Examples of piezoelectric fuel injectors are disclosed in U.S. Pat. Nos. 4,101,076 and 4,635,849, the entire disclosures of which are hereby incorporated herein by reference. Piezoelectric fuel injectors are well-known for use in automotive engines.
The metering of fuel with a piezoelectric fuel injector is generally achieved by controlling the electrical voltage potential applied to the piezoelectric elements to thereby vary the amount of expansion and contraction of the piezoelectric elements. The amount of expansion and contraction of the piezoelectric elements varies the travel distance of a valve needle and, thus, the amount of fuel that is passed through the fuel injector.
Piezoelectric fuel injectors offer the ability to precisely meter a small amount of fuel. However, piezoelectric fuel injectors also require relatively high voltages and high currents in order to function properly. Known conventional drive circuitry for controlling a piezoelectric fuel injector is generally complicated and usually requires extensive energy. Additionally, many prior piezoelectric injector drive circuits generally do not optimize injector performance over a wide operating range of the engine.
Accordingly, it is therefore desirable to provide for a less complicated and more energy efficient drive circuit for driving a piezoelectric injector, such as a fuel injector for injecting fuel into an engine. It is also desirable to provide a drive circuit that offers enhanced operation of the piezoelectric injector over a wide range of engine operating points (e.g., engine speed, load, etc.).
In accordance with the teachings of the present invention, a drive circuit is provided for controlling a piezoelectric injector. According to one aspect of the present invention, the drive circuit includes a voltage input for receiving a voltage signal and a bidirectional current path coupled to a piezoelectric injector. The drive circuit also includes an inductor coupled in series with the bidirectional current path and switching circuitry for controlling current flow through the piezoelectric injector and the inductor. The switching circuitry is controlled to operate the piezoelectric injector by causing current to flow in a first direction in the bidirectional current path to discharge the injector and by causing current to flow in a second direction in the bidirectional current path to charge the piezoelectric injector.
According to another aspect of the present invention, the drive circuit includes a voltage input for receiving a voltage signal, an energy storage device coupled to the voltage input for storing an electrical charge, a bidirectional current path coupled to a piezoelectric injector, an inductor coupled in series with the bidirectional current path, and switching circuitry for controlling current flow through the piezoelectric injector and the inductor. The switching circuitry is controlled to open and close the piezoelectric injector and is controlled to provide a recirculation current to recover energy stored in the piezoelectric injector for storage in the energy storage device. By recovering energy stored in the piezoelectric injector, an enhanced energy efficient piezoelectric injector drive circuit is provided. The drive circuit is particularly well-suited for driving a piezoelectric fuel injector for injecting fuel in an engine.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims and appended drawings.